1. Field of the Invention
This invention relates to methods and apparatus for exploring the subsurface of the earth for valuable deposits of oil and/or gas, of other minerals and of geothermal energy resources by using some direct manifestation of the presence of such deposits, namely perturbations in the earth magnetic field created by the electro-telluric currents generated spontaneously by such deposits.
2. Description of the Prior Art
There are numerous exploration systems that have been proposed for locating in the earth deposits of oil and/or gas, of other minerals and of geothermal energy resources by outlining favorable geologic features such as structural (deformational) and/or stratigraphic (sedimentational) regions of entrapment or accumulation on the basis of favorable statistical association of such deposits with the said geologic features. However, there is no satisfactory system of exploration for such deposits that utilizes direct observation of physical and chemical properties, and of modifications of the lithologic environment in which such deposits are found, and in which the mode of migration and of accumulation of the minerals was responsible for geophysicochemical modifications created by the mere presence of such deposits.
Some exploration techniques, classed as geochemical prospecting, that use analysis of soil-air for hydrocarbon traces or that use the analysis of actual soils for the presence of absorbed light and heavy hydrocarbons, have been and they are still practiced with moderate success, but in view of the near surface nature of these observations, many disturbing factors are present in the measurements. Soil-air and soil analysis have not given the high success ratio in exploring for oil and/or gas that would be expected from a direct discovery technique and this geochemical method is not generally accepted as a satisfactory exploration method.
Geochemical exploration for minerals has generally proved satisfactory for discovering mineral deposits at shallow depths (of the order of 1000 feet), but for greater depths it has proved of little value.
Exploration for geothermal energy resources is in its infancy and no satisfactory method is known up to this point in time which can pin-point superheated steam reservoirs at depths of one to two miles, or can delineate in the subsurface the boundaries of geothermal energy resources of magmatic origin.
Magneto-electric exploration is not to be confused with the Hayes patents of reference (U.S. Pat. No. 2,368,217 and U.S. Pat. No. 2,368,218) because these patents teach only the methods of detecting the electric currents generated by oil and gas fields by measuring the omhic potential drop effects at the surface of the earth and without giving a satisfactory explanation for the origin of said currents nor for their flow patterns. Nor should magneto-electric exploration be confused with the magneto-telluric method of Cagniard (U.S. Pat. No. 3,514,693) which records continuously the micropulsations of both the related magnetic and electric fields of the earth at one point, or simultaneously at two points in order to make deep crustal studies of the earth to depths of 50 to 100 Km for the purpose of determining rock resistivities at such depths. In magneto-telluric studies it is necessary to measure two magnetic field components in the direction perpendicular to the direction of the measured electric field. When two stations are used, this requires at least a four trace continuous recorder. In addition a time-maker needs to be recorded. While the method of Cagniard may be used for shallower depths of investigation it is useless for the finding of oil directly, for all it is able to measure is earth resistivity as a function of depth on a very coarse scale and it lacks the fine vertical resolution required to find oil.